Sometimes in purchasing the invoice in specific period is received after the VAT reporting period.
My suggestion is to make the existing date as an accounting date, and make another cell to be the invoicing date for record only. That will make the VAT report is more accurate.
Why do you consider this to be an issue? Simply enter the supplier’s sales invoice date as the date of the purchase invoice. The fact that the date field is prefilled with the current date is irrelevant. Accounting records are often entered after the fact.